Along with the increase in communication demand, more effective communication path control functionality is demanded of Layer 2 switches that forward packets on a network. For example, the spanning tree protocol is established as a communication path control technique. However, in order to keep a communication path from becoming a loop, the spanning tree protocol produces blocking ports by limiting the communication path candidates to a tree. For this reason, there exists a problem in that effective bandwidth utilization becomes difficult, for example.
Meanwhile, the Transparent Interconnection of Lots of Links (TRILL) technology stipulated by the Internet Engineering Task Force (IETF) is gaining prevalence as a communication path control technique. TRILL technology is characterized by a Shortest Path First (SPF) algorithm that determines a communication path that minimizes the total of costs that signify the communication rate of each link, and an Equal Cost Multi Path (ECMP) algorithm that allows traffic distribution when multiple such communication paths exist. Relevant literature of the related art includes D. Eastlake: “Transparent Interconnection of Lots of Links (TRILL) Use of IS-IS”, IETF RFC 6326, July 2011, R. Perlman: “Routing Bridges (RBridges): Base Protocol Specification”, IETF RFC 6325, July 2011, D. Eastlake 3rd, “Routing Bridges (RBridges): Adjacency”, IETF RFC 6327, July 2011, and R. Perlman: “Routing Bridges (RBridges): Appointed Forwarders”, IETF RFC 6439, November 2011.